The present invention relates to hydraulic excavators and pertains particularly to a linkage arrangement obtaining optimum power from an excavator.
Hydraulic excavators have come into widespread use because of their versatility for application in the construction industry. In many of these applications, it is desirable to apply more power to the bucket than is available from linkage of the particular machine. The prior art machines have not been designed to utilize the linkage in a manner to apply the maximum power that it is capable of handling.
This is especially so when the excavator is being operated with a front opening or front loading bucket. Such prior art excavators have failed to utilize the most efficient arrangement of linkage and power cylinders.
The excavator applies power to the bucket for cutting and the like solely through the manipulation of linkages, with the vehicle normally kept or maintained in a stationary position. This is in contrast to the usual loader machine wherein force or power is applied to the bucket for loading purposes by translation of the vehicle itself along the ground. In other words, power is applied to the excavator bucket by means of hydraulically operated linkages, whereas power is applied to the loader type bucket by means of the driving wheels of the vehicle. Thus, the movement of the bucket in an excavator is controlled during its operation through the manipulation of the linkage system.
The application of power to the bucket by means of the linkage system requires careful and precise control of the linkage itself in order to achieve proper manipulation of the bucket. An excavator normally employs a scissors-like linkage arrangement having a boom pivoted at one end of the excavator vehicle, and a stick pivoted at one of its ends to the outer end of the boom, and a bucket pivoted to the outer end of the stick. Hydraulic rams or motors are operatively connected for operation of each of the boom, stick and bucket, and are each provided with a separate control valve manipulated by the operator to control the respective motor.
One major problem with the prior art linkages is that the geometry thereof does not lend itself to the maximum application of force or power through the linkage. In other words, the linkage is normally arranged to move the bucket in the desired path and to apply some minimum satisfactory amount of power to the bucket. The maximum power capabilities of such prior art linkages then become the maximum power of their weakest link.
Force diagrams on prior linkages indicate that while many of them have optimum location of one or more of the components of the linkage, they fail to provide an optimum linkage arrangement for all components. Thus, they fail to take advantage of the possibility of transmitting the maximum amount of power through the linkage to the bucket. A front loading bucket, for example, should be able to develop almost enough power upon forward movement of the bucket to skid the tracks of the vehicle along the ground. It should be able to develop this much power without excessive-size hydraulic jacks within the linkage or without bending or breaking the linkage. Similarly, the linkage should be able to lift or apply an upward lift to the linkage that is sufficient to tilt the vehicle on its tracks. In order to accomplish this, an optimum arrangement of the linkage is necessary with an optimum location of the power cylinders.
The prior art is exemplified by the following U.S. Pat. Nos. 3,578,188 issued May 11, 1971; 3,570,691 issued Mar. 16, 1971; 3,536,216 issued Oct. 27, 1970; 3,028,026 issued Nov. 20, 1959; 2,852,149 issued Sept. 16, 1958; and British specification No. 1,200,133, which was published July 29, 1970.